import pandas as pd
df = pd.DataFrame({'商品':['苹果','香蕉','梨'],
                   '单价(元)':[5,5,4],
                   '销量(kg)':[100,None,None],
                   '库存(kg)':[50,None,70]})
print('原始数据: \n',df)
print('检查缺失值: \n',df.isnull())
print('检查非缺失值: \n',df.notnull())
print('统计每列缺失值的个数: \n',df.isnull().sum())